Poly(arylene ether) resins are well known and widely used thermoplastics valued for properties including heat resistance, stiffness, and high impact strength. Various methods of preparing poly(arylene ether) homopolymers and copolymers are known, such as the self-condensation of a monovalent phenol in the presence of an oxygen-containing gas, and a catalyst. When primary or secondary amines are used in the reaction process, the amine may become incorporated into the poly(arylene ether) in the form of Mannich end groups. See, for example, U.S. Pat. No. 4,477,651 to White et al., U.S. Pat. No. 4,092,294 to Bennett, Jr. et al., and D. M. White and S. A. Nye, Macromolecules (1990), vol. 23, no. 5, pages 1318-1329. A general reaction scheme for amine incorporation in poly(arylene ether) is shown below: 
Incorporated amine groups may serve a desired function. For example, the amine groups may be lost thermally during processing or blending, resulting in the generation of reactive functional groups on the polymer, such as quinone methide groups. These reactive functional groups can couple with each other to increase the molecular weight of the poly(arylene ether). When the poly(arylene ether) is blended with another resin (e.g., rubber, high impact polystyrene, polyamide), the reactive functional groups can react with the other resin to generate a graft copolymer that improves the physical properties of the resin blend. The formation of such graft copolymers is particularly useful for compatibilizing blends of poly(arylene ether) and polyamide resins.
Current methods of producing poly(arylene ether)s include solution polymerization and precipitation methods. An example of a precipitation method is found in European Patent Application No. 153,074 A2 to Kawaki et al., which generally describes a process for producing a poly(arylene ether) employing a catalyst composed of a cuprous salt and a primary or secondary amine in a mixed solvent consisting of 1 part by weight of a good solvent for the resulting poly(arylene ether) and 0.9 to 1.1 part by weight of a poor solvent for the resulting poly(arylene ether). The poly(arylene ether) is described as precipitating during the polymerization, and it is isolated by filtration and washing. The amount of amine incorporation is not mentioned.
An example of a solution polymerization method includes U.S. Pat. No. 4,477,651 to White et al., which generally describes the preparation of polyphenylene ethers by oxidatively coupling a phenolic compound in the presence of a catalyst which comprises a copper complex of a copper compound with an N,N-disubstituted alkylene or cycloalkylene diamine, a tertiary amine, a bromine-containing-compound, and dimethyl amine. Short reaction times were obtained, and the high molecular weight product increased in molecular weight and showed a marked decrease in bound nitrogen after molding. Bound amine prior to molding was present at levels of up to 1040 parts per million, measured as atomic nitrogen.
The above methods of preparing poly(arylene ether)s do not describe how to control the incorporation of amine groups into a poly(arylene ether). There remains a need for an economical, scalable method for the production of poly(arylene ether) resins having a substantial and reproducible content of incorporated amine.
The above-described and other drawbacks and disadvantages of the prior art are alleviated by a method of preparing a poly(arylene ether), comprising oxidatively coupling a monohydric phenol at a reaction temperature, Trxn, using an oxygen-containing gas in the presence of a solvent and a complex metal catalyst to produce a reaction mixture comprising a poly(arylene ether) resin; wherein the reaction mixture has a cloud point, Tcloud; and wherein Trxn is greater than Tcloud.
In another embodiment, a method of preparing a poly(arylene ether), comprises oxidatively coupling 2,6-dimethylphenol and 2,3,6-trimethylphenol at a reaction temperature, Trxn, using an oxygen-containing gas in the presence of toluene and a complex copper catalyst to produce a reaction mixture comprising a poly(arylene ether) copolymer resin; wherein Trxn satisfies the inequality       T    rxn     greater than       (                            φ          s                -                  (                                    0.296              xc3x97              IV                        +                          1.27              xc3x97              TMP                        -            35.7                    )                            1.97        ⁢                  (                      1            -                          0.00795              xc3x97              IV                        -                          0.0249              xc3x97              TMP                                )                      )  
where xcfx86s is the copolymer concentration (expressed in weight percent), IV is the intrinsic viscosity of the copolymer in chloroform at 25xc2x0 C. (expressed in mL/g), and TMP is the 2,3,6-trimethylphenol content of the copolymer (expressed in weight percent).
The present inventors have discovered that the precipitation of a poly(arylene ether) resin in a reaction mixture may interfere with amine incorporation reactions. The method is therefore particularly useful for the preparation of poly(arylene ether) copolymers having reduced solubility compared to the homopolymer poly(2,6-dimethyl-1,4-phenylene ether). This method is also useful for the preparation of poly (arylene ether) homopolymers in a mixed solvent system in which the homopolymer has less solubility than it would in an aromatic solvent alone. The method is also particularly suitable for industrial scale reactions, where the desire for high throughput may dictate high concentrations of poly(arylene ether) in the reaction mixture.
Other embodiments, including poly(arylene ether) resins prepared according to the methods, are described below.